Golf ball with improved directional stability in putting stroke

ABSTRACT

A golf ball having a predetermined radius, and a spherical outer surface with a multiplicity of dimples formed therein, wherein said spherical outer surface has at least one hit portion which has a diameter of 5-15 mm. The hit portion may be an undimpled portion in which the dimples are absent; a single-dimple portion in which the dimples are absent except a single one of the dimples that is located at a central part thereof; a groove portion in which a plurality of grooves are formed; or an increased contact-area portion in which a protrusion is formed in each dimple.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates in general to improvements in agolf ball.

[0003] 2. Discussion of the Related Art

[0004] There is known a golf ball consisting principally of, forexample, a spherical body having a certain degree of elasticity, and arubber-made cover covering an outer surface of the spherical body. Thespherical body includes a rubber-made, spherical core which is woundwith a rubber thread or other fiber. In an outer surface of therubber-made cover, there are formed a multiplicity of shallow recessesor dimples each having, in general, a substantially circular shape whosediameter is about 1-3 mm, such that the dimples are distributedsubstantially evenly over the entire outer surface of the cover. Thedimples assist the ball, when hit by a club, to fly high and straight ina golf course. That is, the dimples serve to increase the flightdistance and the directional stability of the ball.

[0005] In the following description, the term “golf course” isinterpreted to mean a golf course area excluding a green, unlessotherwise specified.

[0006] In general, a putter is used as a club for putting in a green ofthe golf course. It is considered important, in a putting play, to set ahitting surface of the putter to be perpendicular to a desired directionin which the ball is intended to run, namely, to be perpendicular to aline to a target hole which line is determined on the basis of variousfactors such as influences of grass grain upon the ball, and to thenswing the putter to stroke the ball parallel to the determined line.However, even if the putter is swung or stroked straight and parallel tothe determined line, the ball does not necessarily run along the line,resulting in difficulty of making the ball run in the desired directionwith a sufficient stability. Such a difficulty of controlling thedirection of the ball tends to be increased, particularly, in a puttingstroke with what is called a “soft touch”, in which the ball is hit witha comparatively small hitting force.

[0007] Various experiments conducted by the present inventors forstudying about the above-described problem revealed that dimples formedin the outer surface of the ball make it difficult to putt the ball inthe desired direction with a sufficient stability. A pressed area of theouter surface of the ball, which is pressed by a face of a club as theball is hit by the club, is elastically deformed to become substantiallyflat, and a reaction force is then generated as a result of the elasticdeformation in the pressed area. This reaction force which restores thepressed area to its original shape, i.e., a part-spherical face servesas a thrust force for thrusting or moving the ball. In this instance,strictly speaking, the pressed area does not become entirely flat due tothe presence of the dimples, and some protrusions and recesses remain inthe pressed area. The thrust force is generated by a comparativelyprotruding area of the pressed area which is located between thedimples, namely, by a contact area of the pressed area which is actuallybrought in contact with the club face. The thrust force is not generatedby the other area of the pressed area which is not actually brought incontact with the club face.

[0008] In a putting stroke, in which the ball is generally hit with acomparatively small hitting force, the above-described pressed areagenerally has a diameter so small as about 5-15 mm, for example, about10 mm, so that the dimples each having a diameter of about 1-3 mm arenot necessarily distributed evenly within Such a small pressed area,unless the dimples and the pressed area are intentionally positionedrelative to each other. The uneven distribution of the dimples withinthe pressed area means that the center of balance of the contact area ofthe pressed area which is actually brought into contact with the clubface, i.e., the center of distribution of the reaction force applied tothe club face from the ball deviates from the center of thecircular-shaped pressed area, whereby the reaction force does not act ina direction parallel to a direction in which the club is swung orstroked, resulting in difficulty of making the ball run in the desireddirection with a sufficient stability.

SUMMARY OF THE INVENTION

[0009] It is therefore an object of the present invention to provide agolf ball which is capable of minimizing the deviation of the center ofbalance of the contact area from the center of the pressed area, so thatthe ball is made to run in a desired direction with an improvedstability.

[0010] The above object may be achieved according to a first preferredform of the present invention, which provides a golf ball having apredetermined radius, and a spherical outer surface with a multiplicityof dimples formed therein, wherein the spherical outer surface has atleast one hit portion which has a diameter of 5-15 mm and within whichthe dimples are absent.

[0011] When the golf ball constructed according to the first preferredform of the invention is pressed at any one of the above-described atleast one hit portion by a face of a club, the hit portion becomessubstantially flat with substantially no protrusions and recessestherein, owing to the absence of the dimples within the hit portion, andis brought into contact in its entirety with the club face, so that thecenter of distribution of the reaction force of the ball substantiallycoincides with the center of the pressed area. In other words, the hitportion, i.e., the undimpled portion having the diameter of at least 5mm provides a flat portion having a diameter of at least 5 mm, withinthe pressed area which has a diameter of about 5-15 mm in a puttingstroke, whereby a sufficiently increased part of the pressed area isbrought in contact with the club face. That is, a sufficiently increasedcontact area actually brought in contact with the club face is providedwithin the pressed area so that the center of balance of the contactarea substantially coincides with the center of the pressed area.

[0012] Such a substantial coincidence of the center of distribution ofthe reaction force and the center of the pressed area is obtained evenwhere the diameter of the pressed area is made larger than the diameterof the hit portion, namely where some part of the pressed area is notbrought in contact with the club face. Therefore, the reaction forceacts in a direction substantially parallel to a direction in which theclub is swung or stroked, irrespective of the amount of the hittingforce. It is noted that the diameter of the hit portion may beinterpreted to mean a diameter as seen in projection by parallel raysemitted in a direction parallel to a straight line connecting the centerof the hit portion and the center of the ball.

[0013] As described above, the dimples serve to advantageously increasethe flight distance of the ball and improve the directional stability ofthe ball. These advantageous effects provided by the dimples are not soinfluenced by the undimpled hit portion. That is, the influences of theundimpled hit portion upon the flight distance and the directionalstability of the ball are negligibly small, since the maximum diameterof the undimpled hit portion is as small as about 15 mm.

[0014] It is not possible to control the ball, which has been hit, to bestopped such that the undimpled hit portion of the ball is positioned ina desired position relative to a target hole. However, it is possible toadjust the position of the undimpled hit portion of the ball relative tothe target hole when the ball is replaced at a stopped position on agreen, on which the ball is allowed to be picked up after the stoppedposition is marked. Thus, the ball can be put on the green such that thecenter of the hit portion is positioned on a predetermined line to thetarget line and such that the center of the hit portion is remoter fromthe target hole than the center of the ball, so that the undimpled hitportion serves as the pressed area to be pressed by the club face in aputting stroke.

[0015] It might be possible to putt a conventional ball (which does nothave a particular portion equivalent to the hit portion) in a desireddirection, by pressing a suitable point of the outer surface of theconventional ball by a putter face such that the dimples are distributedevenly in the entirety of the pressed area, namely, such that the centerof balance of the contact area substantially coincides with the centerof the pressed area. However, the diameter of the pressed area in aputting stroke is so small that the distribution of the dimples or thecenter of balance of the contact area is easily changed or displacedeven with a small amount of deviation of an actually pressed point fromthe above-described suitable point. Thus, for making the conventionalball run in a desired direction, it is necessary to accurately locatethe suitable point and then press the ball precisely at the suitablepoint, which are extremely difficult to be done by a golf player duringhis putting play.

[0016] According to one advantageous arrangement of the first preferredform of the invention, the above-described at least one hit portionconsists of a plurality of hit portions which are positioned relative toeach other such that a center of balance of the plurality of hitportions coincides with the center of the golf ball. This balancedarrangement of the hit portions permits the golf ball to enjoy anaerodynamic uniformity, during its flight in a golf course, as aconventional ball which does not have the undimpled hit portions,thereby minimizing a negative aerodynamic effect and preventing areduction of the flight distance.

[0017] The above object may be also achieved according to a secondpreferred form of the present invention, which provides a golf ballhaving a predetermined radius, and a spherical outer surface with amultiplicity of dimples formed therein, wherein the spherical outersurface has at least one hit portion which has a diameter of 5-15 mm andwithin which the dimples are absent except a single one of the dimplesthat is located at a central part of the hit portion.

[0018] In the hit portion of the golf ball of the second preferred formof the invention, the single dimple is located at the central part ofthe hit portion, and an annular part of the hit portion surrounding thecentral part constitutes a part of the spherical outer surface. When thegolf ball of the second preferred form of the invention is pressed atthe hit portion by a club face, the annular part of the hit portionbecomes substantially flat with substantially no protrusions andrecesses therein, and is brought into contact with the club face, sothat the center of distribution of the reaction force of the ballsubstantially coincides with the center of the pressed area. In otherwords, the hit portion, i.e., the single-dimple portion having thediameter of at least 5 mm provides an annular-shaped flat portion havinga diameter of at least 5 mm, in the pressed area which has a diameter ofabout 5-15 mm in a putting stroke, whereby a sufficiently increasedcontact area actually brought in contact with the club face is providedin the pressed area so that the center of balance of the contact areasubstantially coincides with the center of the pressed area.

[0019] Such a substantial coincidence of the center of distribution ofthe reaction force and the center of the pressed area is obtained, evenwhere the center of the pressed area does not exactly coincide with thecenter of the hit portion, or even where the diameter of the pressedarea is made larger than the diameter of the hit portion, namely wheresome part of the pressed area is not brought in contact with the clubface. Therefore, the reaction force acts in a direction substantiallyparallel to a direction in which the club is swung or stroked, so thatthe ball is made to run in a desired direction substantially equal tothe direction in which the club is stroked.

[0020] The hit portion of the golf ball of the second preferred form ofthe invention has the single dimple located at the center part, whilethe hit portion of the golf ball of the first preferred form does nothave any one of the dimples. This means that the golf ball of the secondpreferred form has a smaller area in which the dimples are absent, thanthat of the golf ball of the first preferred form, thereby furtherminimizing a negative aerodynamic effect. Further, the golf ball of thesecond preferred form is advantageous over the golf ball of the firstpreferred form, for minimizing a negative sensuous effect. For example,the smaller undimpled area provides a better appearance of the ball. Theprovision of the single dimple in the hit portion provides a better hitsound in a putting stroke, since the ball is hit at the central part ofthe hit portion at which the single dimple is located.

[0021] The above object may be also achieved according to a thirdpreferred form of the present invention, which provides a golf ballhaving a predetermined radius, and a spherical outer surface with amultiplicity of dimples formed therein, wherein the spherical outersurface has at least one hit portion which has a diameter of 5-15 mm andwithin which the dimples are absent and a plurality of grooves areformed to be distributed evenly in the entirety of the hit portion, eachof the grooves having a predetermined shape and a width which is smallerthan a diameter of each of the dimples.

[0022] In the hit portion of the golf ball of the third preferred formof the invention, the dimples are absent while the grooves each havingthe width smaller than the diameter of each dimple are formed to bedistributed evenly in the entirety of the hit portion. Where the golfball is pressed at this hit portion by a club face, the deviation of thecenter of balance of the contact area from the center of the pressedarea tends to be reduced more than where the golf ball is pressed at theother portion of the spherical outer surface in which the dimples eachhaving the diameter larger than the width of each groove are formed.Thus, by hitting the ball at the hit portion in a putting stroke, it ispossible to make the center of the pressed area substantially coincidewith the center of distribution of the reaction force, so that thereaction force acts in a direction substantially parallel to a directionin which the club is swung or stroked, whereby the ball is made to runin a desired direction substantially equal to the direction in which theclub is stroked.

[0023] In the golf ball of the third preferred form of the invention, anegative aerodynamic effect is more reduced, owing to the provision ofthe grooves or recesses in the hit portion, than in the golf ball of thefirst preferred form having the undimpled hit portion in which any oneof the dimples or recesses is not formed.

[0024] According to a first advantageous arrangement of the thirdpreferred form of the invention, the grooves are arranged in a latticeand intersect each other, so that the grooves formed in the hit portionare symmetrical with each other. The lattice or symmetrical arrangementof the grooves further reduces the deviation of the center ofdistribution of the reaction force from the center of the pressed area,where the center of the pressed area is deviated from the center of thehit portion, i.e., where the golf ball is not hit at the center of thehit portion. Thus, the arrangement of this first advantageousarrangement is effective to further improve the directional stability ofthe ball in a putting stroke.

[0025] According to a second advantageous arrangement of the thirdpreferred form of the invention, the grooves are annular grooves havingrespective diameters different from each other and respective centerslying at a center of the hit portion, so that the grooves are held in aconcentric relationship with each other. This concentric arrangement ofthe grooves also further reduces the deviation of the center ofdistribution of the reaction force from the center of the pressed area,where the center of the pressed area is deviated from the center of thehit portion. Thus, the arrangement of this second advantageousarrangement is also effective to further improve the directionalstability of the ball in a putting stroke.

[0026] According to a third advantageous arrangement of the thirdpreferred form of the invention, the grooves are arranged to be parallelto each other. This parallel arrangement of the grooves also furtherreduces the deviation of the center of distribution of the reactionforce from the center of the pressed area, where the center of thepressed area is deviated from the center of the hit portion. Thus, thearrangement of this third advantageous arrangement is also effective tofurther improve the directional stability of the ball in a puttingstroke. Further, the arrangement of this third advantageous arrangementprovides another advantage of minimizing undesirable displacement of thecenter of balance of the contact area relative to the center of thepressed area, by setting the ball on a green such that the parallelgrooves are brought in parallel to the vertical or horizontal directionin a preparation for a putting stoke, even if the center of the pressedarea is deviated from the center of the hit portion in the puttingstroke.

[0027] The above object may be also achieved according to a fourthpreferred form of the present invention, which provides a golf ballhaving a predetermined radius, and a spherical outer surface with amultiplicity of dimples formed therein, wherein the spherical outersurface has at least one hit portion which has a diameter of 5-15 mm andwithin which a protrusion is formed in each of the dimples, theprotrusion having a distal end whose radial distance from the center ofthe golf ball is equal to the predetermined radius of the golf ball.

[0028] In the hit portion of the golf ball of the fourth preferred formof the invention, the protrusions, each having the distal end whoseradial distance from the center of the golf ball is equal to thepredetermined radius of the golf ball, are formed in the respectivedimples. Where the golf ball is pressed at this hit portion by a clubface, the protrusion constituting a part of area inside each dimple, aswell as an area surrounding each dimple, is brought in contact with theclub face, thereby providing a sufficiently increased contact areawithin the pressed area and accordingly minimizing the deviation of thecenter of balance of the contact area from the center of the pressedarea, so that the center of balance of the contact area substantiallycoincides with the center of the pressed area. Thus, by hitting the ballat the hit portion in a putting stroke, it is possible to make thecenter of the pressed area substantially coincide with the center ofdistribution of the reaction force, so that the reaction force acts in adirection substantially parallel to a direction in which the club isswung or stroked, whereby the ball is made to run in a desired directionsubstantially equal to the direction in which the club is stroked.

[0029] In the golf ball of the fourth preferred form of the invention, anegative aerodynamic effect and a negative sensuous effect such asdeterioration of the appearance are more reduced, owing to the provisionof the dimples in the hit portion as well as in the other portions ofthe spherical outer surface of the golf ball, than in the golf ball ofthe first preferred form having the undimpled hit portion in which anyone of the dimples is not provided.

[0030] According to a first advantageous arrangement of the fourthpreferred form of the invention, the protrusion is positioned relativeto each of the dimples such that the protrusion has a concentricrelation with each of the dimples.

[0031] According to a second advantageous arrangement of the fourthpreferred form of the invention, the protrusion has a partition wallwhich divides a space in each of the dimples into a plurality ofsegmental spaces.

[0032] In either of the first and second arrangements of the fourthpreferred form, a sufficiently increased contact area actually broughtin contact with a club face is provided in the pressed area, and thedirectional stability of the ball in a putting stroke is accordinglyimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above object, features and advantages of the presentinvention will be better understood by reading the following detaileddescription of presently preferred embodiments of the invention, whenconsidered in connection with the accompanying drawings, in which:

[0034]FIG. 1(a) is a view showing a golf ball according to a firstembodiment of this invention;

[0035]FIG. 1(b) is a view for explaining the arrangement of undimpledportions provided on the surface of the golf ball of FIG. 1(a);

[0036]FIG. 2(a) is an upper plan view showing the golf ball of FIG. 1(a)at an impact moment when the golf ball is hit by a putter;

[0037]FIG. 2(b) is a view taken in a direction of arrow b of FIG. 2(a);

[0038] FIGS. 3(a) and (b) are views illustrating examples of a contactarea at which a conventional golf ball is brought in contact with aputter face;

[0039]FIG. 4 is a view for explaining an experiment conducted forconfirming influences of dimples of a conventional ball upon arebounding direction of the conventional ball;

[0040]FIG. 5 is a view illustrating a contact area of the conventionalball which was actually brought in contact with a flat horizontalsurface when the ball was dropped from each of various height levels inthe experiment of FIG. 4;

[0041]FIG. 6 is a view showing a golf ball according to a secondembodiment of this invention;

[0042]FIG. 7 is a view corresponding to that of FIG. 2(b) and taken fromthe side of a pressed area, for showing the ball of FIG. 6 at an impactmoment when the ball is hit at the pressed area;

[0043]FIG. 8 is a view showing a golf ball according to a thirdembodiment of this invention;

[0044]FIG. 9 is a view showing a golf ball according to a fourthembodiment of this invention;

[0045]FIG. 10 is a view showing a golf ball according to a fifthembodiment of this invention;

[0046]FIG. 11 is a view showing a golf ball according to a sixthembodiment of this invention;

[0047]FIG. 12(a) is a view showing a golf ball according to a seventhembodiment of this invention;

[0048]FIG. 12(b) is an enlarged view showing a part of the surface ofthe ball of FIG. 12(a);

[0049]FIG. 12(c) is a view showing a cross section of theabove-described part of the surface of the ball of FIG. 12(a);

[0050]FIG. 13(a) is a view showing a golf ball according to an eighthembodiment of this invention; and

[0051]FIG. 13(b) is an enlarged view showing a part of the surface ofthe ball of FIG. 13(a).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Referring first to FIGS. 1(a) and (b), there is shown a golf ball10 of a first embodiment of this invention which is constructed inaccordance with golf international standards. The golf ball 10 has apredetermined radius, and is made of a rubber material similar to thatused in conventional golf balls to have a certain degree of elasticity.The golf ball 10 has, in its spherical outer surface 12, a multiplicityof shallow depressions or dimples 14 formed to be arranged according toa predetermined pattern. Each of the dimples 14 has a substantiallycircular shape whose diameter is about 1-3 mm.

[0053] In the major portion of the spherical outer surface 12 of theball 10, the spacing interval between adjacent ones of the dimples 14 isnot larger than, for example, about 1 mm. However, in local portions ofthe spherical outer surface 12, the spacing interval between theadjacent dimples 14 is increased to, for example, about 10 mm. That is,the spherical outer surface 12 has, in its local portions, substantiallycircular-shaped undimpled portions 16 in each of which the dimples 14are not formed. Each undimpled portion 16 is dimensioned such that acircle having a diameter of about 10 mm is inscribed in the undimpledportion 16. In the golf ball 10 of the present embodiment, the sphericalouter surface 12 has six undimpled portions 16 which are symmetricallyarranged as shown in FIG. 1(b). Specifically described, the undimpledportions 16 a, 16 b are arranged so as to lie on X-axis, which is one ofthree axes perpendicular to each other and meet at the center of theball 10, so as to be symmetrical with each other with respect to thecenter of the ball 10. The undimpled portions 16 c, 16 d are arranged tolie on Y-axis to be symmetrical with each other with respect to thecenter of the ball 10. The undimpled portions 16 e, 16 f are arranged tolie on Z-axis to be symmetrical with each other with respect to thecenter of the ball 10.

[0054] It is noted that each of the undimpled portions 16, which isrepresented by a circle in FIG. 1(b), is defined by profiles of ones ofthe dimples 14 surrounding the undimpled portion 16. Thus, eachundimpled portion 16 has a profile consisting of a succession ofrecesses and protrusions arranged alternately in the circumferentialdirection of the undimpled portion 16, wherein the recesses andprotrusions are provided by the profiles of those ones of the dimples 14surrounding the undimpled portion 16. It is also noted that eachundimpled portion 16 has a part-spherical outer surface whichconstitutes a part of the spherical outer surface having a radius R.Namely, the undimpled portions 16 cooperate with the above-describedmajor portion to constitute the spherical outer surface of the ball 10.

[0055]FIG. 2(a) is an upper plan view showing the ball 10 at an impactmoment when the ball 10 is hit at a pressed area 22 of the sphericalouter surface 12, by a putter face 20 of a putter head 18 for puttingthe ball 10 on a green. At the impact moment, the pressed area 22 isdeformed to become a substantially flat face conforming to the putterface 20, due to a friction force acting between the ball 10 and a grassof the green on which the ball 10 lies, and also a pressing forceapplied to the ball 10 from the putter face 20. The pressed area 22 hasa substantially circular shape (whose diameter A is about 5-15 mm), asshown in FIG. 2(b) which is a view taken in a direction of arrow b ofFIG. 2(a). The diameter of the circular-shaped pressed area 22 variesdepending upon amount of a hitting force with which the ball 10 is hit,and tends to be reduced with a reduction of the amount of the hittingforce. The diameter of the pressed area 22 is about 5-15 mm in a puttingstroke in which the ball is generally hit with a comparatively smallhitting force. It is appreciated that the entirety of the pressed area22 is located within one of the undimpled portions 16 in FIG. 2(b). Thatis, in a preparation for putting the ball 10, the ball 10 is put on thegreen while taking account of a direction of stroke of the putter head18, such that one of the undimpled portions 16 serves as the pressedarea 22. In the present embodiment, the undimpled portions 16 correspondto lit portions.

[0056] Since the ball 10 is brought into contact in almost the entiretyof the circular-shaped pressed area 22 with the putter face 20 at theabove-described impact moment, the center of balance of a contact areaactually brought in contact with the putter face 20 substantiallycoincides with the center of the pressed area 22. Describedspecifically, when the ball 10 is pressed at the undimpled portion 16,which has the diameter of about 10 mm and within which the dimples 14are not formed, by the putter face 20, the pressed area 22 becomessubstantially flat with substantially no protrusions and recessestherein, so that the center of distribution of the reaction forceapplied to the putter face 20 from the ball 10 substantially coincideswith the center of the circular-shaped pressed area 22 which is broughtin contact with the putter face 20 so as to become substantially flat.Accordingly, a reaction force, which serves as a thrust force forthrusting or moving the ball 10, is generated based on a restoring forceof the ball 10 for restoring the pressed area 22 to its original shape,i.e., a part-spherical shape, and acts in a direction which issubstantially parallel to a direction P in which the putter head 18 isswung or stroked, on the assumption that the putter face 20 is kept inperpendicular to the direction P during the stroke of the putter head18. The ball 10 runs based on the thrust force in a direction B which issubstantially parallel to the direction P of the stroke of the putterhead 18, thereby making it possible to putt the ball 10 in a desireddirection with an improved stability.

[0057] On the other hand, when a conventional golf ball, in which thedimples are formed to be arranged evenly in its entire spherical outersurface, is hit by the putter face 20, the conventional ball is broughtin contact with the putter face 20, as illustrated in FIG. 3(a) or (b).In FIGS. 3(a) and (b), a circle 24 defined by one-dot chain linerepresents a pressed area at which the conventional ball is hit by theputter face 20, an area 26 indicated by oblique lines represents acontact area of the pressed area 24 which area is actually brought incontact with the putter face 20, and areas 28 indicated by voids orblanks represent the dimples formed in the spherical outer surface.There is a case where the center of the pressed area 24 does notcoincide with the center of balance of the contact area 26, as shown inFIG. 3(a) or (b). In such a case, the center of the pressed area 24 doesnot coincide with the center of distribution of the reaction forceapplied to the putter face 20, so that the running direction of the balldoes not coincide with the stroke direction of the putter head 18. Therunning direction is undesirably variable depending upon how the ball isbrought in contact with the putter face 20, thereby making it difficultto putt the ball in a desired direction with a high stability.

[0058] As described above, the undimpled portions 16 are arranged to besymmetrical with each other with respect to the center of the golf ball10, so that a center of balance of the undimpled portions 16 coincideswith the center of the ball 10. This arrangement of the undimpledportions 16 permits the ball 10 to enjoy an aerodynamic uniformity,during its flight in a golf course, as the conventional ball which doesnot have the undimpled portions 16. In other words, the symmetrical orbalanced arrangement of the undimpled portions 16 is effective tominimize a negative aerodynamic effect due to the absence of the dimples14 in each undimpled portion 16, thereby avoiding a reduction of theflight distance.

[0059]FIG. 4 shows the result of an experiment conducted by using aconventional golf ball 32 in which the dimples 28 are formed evenly inthe entire spherical outer surface, for confirming influences of thedimples 28 over a direction in which the ball 32 advances, runs orflies. In the experiment, the conventional ball 32 was made to freelyfall from various height levels towards a flat horizontal surface 30having a hardness and other material characteristics similar to those ofthe putter face 20, and variations in an inclination of a reboundingdirection j of the ball 32 with respect to a falling locus g of the ball32 are measured. The j4, j3, j2, j1 and j0.5 represent the respectivemaximum inclinations of the rebounding direction j with respect to thefalling locus g (which are described to be symmetrical with respect tothe falling locus g), when the ball 32 was made to fall from therespective heights of 4 m, 3 m, 2 m, 1 m and 0.5 m. In other words, thej4, j3, j2, j1 and j0.5 represent the respective variations in theinclination of the rebounding direction j with respect to the fallinglocus g when the ball 32 was made to fall from the respective heights.It is appreciated from FIG. 4 that the maximum inclination, i.e., thevariation in the inclination was increased with a reduction in theheight from which the ball 32 was made to fall.

[0060]FIG. 5 illustrates a contact area of the spherical outer surfaceof the ball 32 which area was actually brought in contact with the flathorizontal surface 30 when the ball 32 was made to fall from each of thevarious height levels in the above-described experiment. Eachillustration of FIG. 5 was obtained by applying an ink to the entireouter surface of the ball 32 except the dimples 28 before the ball 32was made to fall. It is considered that the actual contact area of thespherical outer surface of the ball 32 is not necessarily exactlyrepresented by the corresponding illustration, since the ink was notnecessarily applied evenly to the entire spherical outer surface of theball 32.

[0061] In FIG. 5, a circle 34 defined by one-dot chain line represents apressed area of the spherical outer surface of the ball 32 which portionwas pressed by the flat horizontal surface 30 to become flat, while aninked area within the circular-shaped pressed area 34 represents acontact area which was actually brought in contact with the flathorizontal surface 30. As is apparent from FIG. 5, the dimples 28 werenot necessarily distributed evenly in the entirety of the pressed area34. This means that the center of balance of the contact area was likelyto be deviated from the center of the pressed area 34. When the ball 32was made to fall from the comparatively small height, e.g., from aheight not larger than 3 m, the circular-shaped pressed area 34 was sosmall that the amount of the deviation of the center of balance of thecontact area from the center of the pressed area 34 tended to beincreased. However, the deviation amount tended to be reduced with anincrease in the height from which the ball 32 was made to fall, namely,with an increase in the number of the dimples 28 included in the pressedarea 34. The deviation amount was reduced to almost zero, when the ball32 was made to fall from the height of 4 m.

[0062] The above-described inclination of the rebounding direction jwith respect to the falling locus g relates to this “deviation” which iscaused by the presence of the dimples 28 in the spherical outer surfaceof the ball 32. The maximum inclination was increased with the increasein the deviation as a result of the reduction of the pressed area 34when the ball 32 was made to fall from the comparatively small height.The maximum inclination was reduced with the reduction in the deviationas a result of the increase of the pressed area 34 when the ball 32 wasmade to fall from the comparatively large height.

[0063] This means that the influences of the dimples 28 upon thedirection in which the ball 32 advances are reduced with an increase inthe hitting force so that the advance direction of the ball 32 issomewhat stabilized. However, the advance direction of the ball 32 isconsiderably influenced by the dimples 28 when the ball 32 is hit with asmall hitting force, e.g., in a “soft touch” putting stroke so that theadvance direction of the ball 32 is not stabilized. In this view, it ispossible to improve the directional stability even in a soft touchputting stroke, by providing the undimpled portions 16 in the sphericalouter surface of the ball and thereby eliminating or minimizing theinfluences of the dimples, as in the golf ball 10 of the presentembodiment.

[0064] Referring next to FIGS. 6-13, there will be described some othergolf balls constructed according to second, third, fourth, fifth, sixth,seventh and eighth embodiments of this invention. In these embodiments,the same reference numerals as used in the first embodiment of FIGS.1(a) and (b) will be used to identify the elements which are the same asor similar to those in the first embodiment. No redundant description ofthese elements will be provided, in the interest of simplification ofthe description.

[0065]FIGS. 6 and 7 show a golf ball 40 of the second embodiment whichhas single-dimple portions 42 in place of the undimpled portions 16.That is, the spherical outer surface 12 of the ball 40 has sixsingle-dimple portions 42 which are arranged to be symmetrical with eachother with respect to the center of the golf ball 40, in addition to themajor portion in which the spacing interval between adjacent ones of thedimples 14 is not larger than about 1 mm. In each of the sixsingle-dimple portion 42 (three of which are invisible in FIG. 6), thedimples 14 are absent except a single one 14 a of the dimples 14 whichis located at a central part of each of the single-dimple portions 42.Each single-dimple portion 42 is dimensioned such that a circle having adiameter of about 10 mm is inscribed in the single-dimple portion 42.The dimple 14 a located at the central part of the single-dimple portion42 has a diameter of about 1-3 mm and the same shape as the otherdimples 14, and has a concentric relationship with the inscribed circle.Thus, the dimple 14 a has a size sufficiently smaller than that of eachsingle-dimple portion 42. An annular part of each single-dimple portion42 which surrounds the dimple 14 a and which is located between thedimple 14 a and those ones of the dimples 14 surrounding thesingle-dimple portion 42 has a part-spherical outer surface whichconstitutes a part of the spherical outer surface 12 having a radius R.Namely, the annular parts of the respective single-dimple portions 42cooperate with the major portion to constitute the spherical outersurface 12 of the ball 40. Therefore, the single-dimple portion 42 issubstantially identical with the undimpled portion 16 except for theprovision of the single dimple 14 a at the central part of portion.

[0066]FIG. 7 is a view corresponding to that of FIG. 2(b) and taken fromthe side of the pressed area 22, for showing the ball 40 at an impactmoment in a putting stroke. At the impact moment, the pressed area 22 isdeformed to become a flat face conforming to the putter face 20 andhaving a substantially circular shape whose diameter A is about 5-15 mm,as in the case of the ball 10 of the first embodiment. FIG. 7 shows acase where the pressed area 22 is brought in a concentric relationshipwith the substantially circular-shaped single-dimple portion 42, namely,with the single dimple 14 a located at the central part of thesingle-dimple portion 42, and where the entirety of the pressed area 22is located within the single-dimple portion 42. In the presentembodiment, the single-dimple portions 42 correspond to hit portions. Ina preparation for putting the ball 40, the ball 40 is put on the greensuch that one of the single-dimple portions 42 serves as the pressedarea 22.

[0067] Since the ball 40 is brought into contact in almost the entiretyof the circular-shaped pressed area 22 with the putter face 20 at theabove-described impact moment, the center of balance of a contact areaactually brought in contact with the putter face 20 substantiallycoincides with the center of the pressed area 22. Describedspecifically, when the ball 40 is pressed at the single-dimple portion42, which has the diameter of about 10 mm and within which the singledimple 14 a is located at the central part, by the putter face 20, theannular part of the single-dimple portion 42 having an inside diameterof 1-3 mm becomes substantially flat, and is brought into contact withthe putter face 20, so that the center of distribution of the reactionforce applied to the putter face 20 from the ball 40 substantiallycoincides with the center of the circular-shaped pressed area 22.Accordingly, a reaction force, which serves as a thrust force forthrusting or moving the ball 40, is generated based on a restoring forceof the ball 40 for restoring the pressed area 22 to its original shape,i.e., a part-spherical shape, and acts in a direction which issubstantially parallel to the direction P in which the putter head 18 isswung or stroked, on the assumption that the putter face 20 is kept inperpendicular to the direction P during the stroke of the putter head18. The ball 40 runs based on the thrust force in a direction B which issubstantially parallel to the direction P of the stroke of the putterhead 18, thereby making it possible to putt the ball 40 in a desireddirection with an improved stability.

[0068] The single-dimple portion 42 serving as the hit portion in thegolf ball 40 of the present second embodiment has the single dimple 14 aat the central part, while the undimpled portion 16 serving as the hitportion in the golf ball 10 of the above-described first embodiment doesnot have any one of the dimples 14. This means that the golf ball 40 hasa smaller area in which the dimples are absent, than that of the golfball 10, thereby further minimizing a negative aerodynamic effect.Further, the golf ball 40 is advantageous over the golf ball 10, forminimizing a negative sensuous effect. For example, the smallerundimpled area provides a better appearance of the ball. The provisionof the single dimple 14 a in the single-dimple portion 42 provides abetter hit sound in a putting stroke, since the ball 40 is hit at thecentral part of the single-dimple portion 42 at which the single dimple14 a is located.

[0069] As described above, the size of each single-dimple portion 42 issufficiently larger than that of the dimple 14 a which is located withinthe single-dimple portion 42. In other words, the size of the dimple 14a, which does not constitute a part of the spherical outer surface 12,is sufficiently smaller than that of the single-dimple portion 42.Therefore, the above-described substantial coincidence of the center ofdistribution of the reaction force and the center of the pressed area 22is made, even where the center of the pressed area 22 does not exactlycoincide with the center of the single-dimple portion 42, namely wherethe ball 40 is not hit at the center of the single-dimple portion 42.This is because the size of the dimple 14 a located within thesingle-dimple portion 42 is so small that the direction of the reactionforce is kept substantially unchanged even if the center of the pressedarea 22 is somewhat deviated from the center of the single-dimpleportion 42. Further, as in the golf ball 10 of the first embodiment withthe undimpled portions 16, the above-described substantial coincidenceis obtained, even where the diameter A of the pressed area 22 is madelarger than the diameter of the single-dimple portion 42, namely wheresome part of the pressed area 22 is not brought in contact with the clubface 20.

[0070]FIG. 8 shows a golf ball 50 of the third embodiment of the presentinvention. The golf ball 50 has lattice-arranged groove portions 54 inplace of the undimpled portions 16. That is, the spherical outer surface12 of the golf ball 50 has six lattice-arranged groove portions 54 whichare arranged to be symmetrical with each other with respect to thecenter of the golf ball 50, in addition to the major portion in whichthe dimples 14 are provided with the spacing interval between adjacentones of the dimples 14 being not larger than about 1 mm. In each of thesix lattice-arranged groove portions 54 (three of which are invisible inFIG. 8), the dimples 14 are absent while a plurality of grooves 52 areformed. Each of the grooves 52 has a width of, for example, about0.5-1.0 mm which is sufficiently smaller than the diameter of eachdimple 14. The grooves 52 are arranged generally in a lattice, in whichsome of the grooves 52 are parallel to a predetermined direction andspaced apart from each other at a pitch of 2-3 mm between the centers ofthe adjacent ones, and in which the others of the grooves 52 areparallel to a direction perpendicular to the predetermined direction andspaced apart from each other at a pitch of 2-3 mm between the centers ofthe adjacent ones. Each lattice-arranged groove portion 54 isdimensioned such that a circle having a diameter of about 10 mm isinscribed in the lattice-arranged groove portion 54. In the presentthird embodiment, the lattice-arranged groove portions 54 correspond tothe hit portions. The ball 50 is put on the green in a preparation forputting the ball 50, such that one of the lattice-arranged grooveportions 54 serves as the pressed area 22.

[0071] The lattice-arranged groove portion 54 of the ball 50 has thediameter of about 10 mm and the grooves 54 arranged in a lattice. Wherethe ball 50 is pressed at the lattice-arranged groove portion 54 by theputter face 20, the deviation of the center of balance of the contactarea from the center of the pressed area 22 tends to be reduced morethan where the ball 50 is pressed at the other portion of the sphericalouter surface in which the dimples 14 each having the diameter largerthan the width of each groove 52 are formed. Thus, by hitting the ball50 at the lattice-arranged groove portion 54 in a putting stroke, it ispossible to make the center of the pressed area 22 substantiallycoincide with the center of balance of the contact area, i.e., thecenter of distribution of the reaction force applied from the ball 50 tothe putter face 20. Accordingly, the reaction force, which serves as athrust force for thrusting or moving the ball 50, is generated based ona restoring force of the ball 50 for restoring the pressed area 22 toits original shape, i.e., a part-spherical shape, and acts in adirection which is substantially parallel to the direction in which theputter head 18 is swung or stroked, so that the ball 50 runs based onthe thrust force in a direction which is substantially parallel to thedirection of the stroke of the putter head 18, thereby making itpossible to putt the ball 50 in a desired direction with an improvedstability.

[0072] In the golf ball 50 of the present third embodiment, a negativeaerodynamic effect is more reduced, owing to the provision of recessesin the form of the grooves 52 in the lattice-arranged groove portion 54,than in the golf ball 50 of the above-described first embodiment havingthe undimpled portions 16 each constituting a part of the sphericalouter surface 12.

[0073] In the golf ball 50 of the present third embodiment, the grooves52 of the lattice-arranged groove portion 54 are arranged in a latticeso as to be symmetrical with each other. The symmetrical arrangement ofthe grooves 52 further reduces the deviation of the center ofdistribution of the reaction force from the center of the pressed area22, where the center of the pressed area 22 is deviated from the centerof the lattice-arranged groove portion 54, i.e., where the golf ball 50is not hit at the center of the lattice-arranged groove portion 54.Thus, the symmetrical arrangement of the grooves 52 is effective tofurther improve the directional stability of the ball 50 in a puttingstroke.

[0074]FIG. 9 shows a golf ball 60 of the fourth embodiment of thepresent invention. The golf ball 60 has annular groove portions 58 inplace of the lattice-arranged groove portions 54. That is, the sphericalouter surface 12 of the golf ball 60 has six annular groove portions 58(three of which are invisible in FIG. 9) in each of which a plurality ofannular grooves 56 are formed. The annular grooves 56 have respectivediameters different from each other, and are positioned relative to eachother to be held in a substantially concentric relationship with eachother. Each of the annular grooves 56 has a width of, for example, about0.5-1.0 mm which is sufficiently smaller than the diameter of thedimples 14. The concentric annular grooves 56 are radially spaced apartfrom each other at a pitch of, for example, about 1-2 mm between thecenters of the radially adjacent ones. The six annular groove portions58 have a diameter of, for example, about 10 mm, and arranged to besymmetrical with each other with respect to the center of the golf ball60. In the present fourth embodiment, the annular groove portions 58correspond to the hit portions. The ball 60 is put on the green in apreparation for putting the ball 60, such that one of the annular grooveportions 58 serves as the pressed area 22.

[0075] Where the ball 60 is pressed at the selected one of the annulargroove portions 58 by the putter face 20, the deviation of the center ofbalance of the contact area from the center of the pressed area 22 tendsto be reduced, as the ball 50 of the above-described third embodimenthaving the lattice-arranged groove portions 54. Thus, by hitting theball 60 at the annular groove portion 58 in a putting stroke, it ispossible to make the center of the pressed area 22 substantiallycoincide with the center of balance of the contact area, i.e., thecenter of distribution of the reaction force applied from the ball 60 tothe putter face 20, thereby making it possible to putt the ball 60 in adesired direction with an improved stability.

[0076]FIG. 10 shows a golf ball 66 of the fifth embodiment of thepresent invention. The golf ball 66 has parallel groove portions 64 inplace of the lattice-arranged groove portions 54. That is, the sphericalouter surface 12 of the golf ball 66 has six parallel groove portions 64(three of which are invisible in FIG. 10) in each of which a pluralityof grooves 62 arranged to be parallel to each other are formed. Each ofthe grooves 62 has a width of, for example, about 0.5-1.0 mm which issufficiently smaller than the diameter of the dimples 14. The grooves 62are spaced apart from each other at a pitch of, for example, about 2-3mm between the centers of the adjacent ones. The six parallel grooveportions 64 are dimensioned such that a circle having a diameter ofabout 10 mm is inscribed in each of the parallel groove portions 64. Itis noted that a direction in which the grooves 62 of each parallelgroove portion 64 extend is not particularly limited, but is preferablydetermined such that the directions of the grooves 62 of all of theparallel groove portions 64 are symmetrical with each other with respectto the center of the ball 66.

[0077] In the present fifth embodiment, the parallel groove portions 64correspond to the hit portions. The ball 66 is put on the green in apreparation for putting the ball 66, such that one of the parallelgroove portions 64 serves as the pressed area 22. Where the ball 66 ispressed at the selected one of the parallel groove portions 64 by theputter face 20, the deviation of the center of balance of the contactarea from the center of the pressed area 22 tends to be reduced, as theball 50 of the above-described third embodiment having thelattice-arranged groove portions 54. Thus, by hitting the ball 66 at theparallel groove portion 64 in a putting stroke, it is possible to makethe center of the pressed area 22 substantially coincide with the centerof balance of the contact area, i.e., the center of distribution of thereaction force applied from the ball 66 to the putter face 20, therebymaking it possible to putt the ball 66 in a desired direction with animproved stability.

[0078] In the golf ball 66 of the present fifth embodiment, the grooves62 are arranged to be parallel to each other in each of the parallelgroove portion 64. This parallel arrangement provides another advantageof preventing displacement of the center of balance of the contact area,by setting the ball 66 on a green such that the grooves 62 are broughtin parallel to the vertical or horizontal direction in a preparation fora putting stoke, even if the center of the pressed area 22 is deviatedfrom the center of the parallel groove portion 64 in the putting stroke.

[0079]FIG. 11 shows a golf ball 74 of the sixth embodiment of thepresent invention. The golf ball 74 has groove portions 72 in place ofthe lattice-arranged groove portions 54. That is, the spherical outersurface 12 of the golf ball 74 has six groove portions 72 (three ofwhich are invisible in FIG. 11) in each of which a W-shaped groove 68and a M-shaped groove 72 are formed. The W-shaped groove 68 and theM-shaped groove 72 are positioned relative to each other so as to besymmetrical with each other, as shown in FIG. 11. The groove portions 72provide substantially the same advantages as the lattice-arranged grooveportions 54, the annular groove portions 58 and the parallel grooveportions 64 of the third, fourth and fifth embodiments. The grooves 68,70 have the same width as the grooves 52, 56, 62 of these embodiments.The groove portions 72 have the same size as the groove portions 54, 58,64 of these embodiments.

[0080]FIG. 12(a) shows a golf ball 76 of the seventh embodiment of thepresent invention. In the golf ball 76, the dimples 14 are formed to bedistributed evenly in the entirety of the spherical outer surface 12 asin the conventional golf ball 32. However, the spherical outer surface12 of the golf ball 76 has six increased contact-area portions 78 (threeof which are invisible in FIG. 12(a)) which are arranged to besymmetrical with each other with respect to the center of the golf ball76, and each of which is dimensioned such that a circle having adiameter of about 10 mm is inscribed in the increased contact-areaportion 78. In each of the six increased contact-area portions 78, acolumnar protrusion 80 having a circular cylindrical shape is formed ineach of the dimples 14 and extends from a bottom of the dimple 14 in aradial direction of the ball 76, as shown in FIG. 12(b). The columnarprotrusion 80 has, at a distal end thereof, a diameter of about 1-2 mmwhich is equal to about ¼-½ of the diameter of the dimple 14, and has aconcentric relationship with the dimple 14. The distal end of thecolumnar protrusion 80 has a radial distance from the center of the ball76, which distance is equal to the radius of the ball 76. Thus, thedistal end of the columnar protrusion 80 lies on the same surface as thespherical outer surface 12, as best shown in FIG. 12(c) (in which onlyone of the dimples 14 is shown while the other simples 14 actuallylocated in the vicinity of the shown one are not described in theinterest of simplification of the drawing). In the present seventhembodiment, the increased contact-area portions 78 correspond to the hitportions. The ball 76 is put on the green in a preparation for puttingthe ball 76, such that one of the increased contact-area portions 78serves as the pressed area 22.

[0081] In the increased contact-area portions 78 having the diameter ofabout 10 mm, the columnar protrusions 80 are formed in the respectivedimples 14. Where the golf ball 76 is pressed at the selected one of theincreased contact-area portions 78 by the putter face 20, the columnarprotrusion 80 constituting a part of area inside each dimple 14, as wellas an area surrounding each dimple 14, is brought in contact with theputter face 20, thereby leading to a larger contact area provided in thepressed area 22, than where the ball 76 is pressed at the other portionof the spherical outer surface 12 in which the columnar protrusions 80are not provided, so that the deviation of the center of balance of thecontact area from the center of the pressed area 22 tends to be reduced.Thus, by hitting the ball 76 at the increased contact-area portion 78 ina putting stroke, it is possible to make the center of the pressed area22 substantially coincide with the center of balance of the contactarea, i.e., the center of distribution of the reaction force appliedfrom the ball 76 to the putter face 20. Accordingly, the reaction force,which serves as a thrust force for thrusting or moving the ball 76, isgenerated based on a restoring force of the ball 76 for restoring thepressed area 22 to its original shape, i.e., a part-spherical shape, andacts in a direction which is substantially parallel to the direction inwhich the putter head 18 is swung or stroked, thereby making it possibleto putt the ball 76 in a desired direction with an improved stability.

[0082] In the golf ball 76 of the present seventh embodiment of theinvention, a negative aerodynamic effect and a negative sensuous effectsuch as deterioration of the appearance are more reduced, owing to theprovision of the dimples 14 in the increased contact-area portions 78 aswell as in the other portions of the spherical outer surface 12, than inthe golf ball 10 of the above-described first embodiment having theundimpled portions 16 in which any one of the dimples 14 is notprovided.

[0083]FIG. 13(a) shows a golf ball 82 of the eighth embodiment of thepresent invention. In the golf ball 82, the dimples 14 are formed to bedistributed evenly in the entirety of the spherical outer surface 12 asin the conventional golf ball 32. However, the golf ball 82 has sixincreased contact-area portions 84 (three of which are invisible in FIG.13(a)) which are arranged to be symmetrical with each other with respectto the center of the golf ball 82, and each of which is dimensioned suchthat a circle having a diameter of about 10 mm is inscribed in theincreased contact-area portion 84. In each of the six increasedcontact-area portions 84, a cross-shaped partition protrusion 86 isformed in each of the dimples 14 and extends from a bottom of the dimple14 in a radial direction of the ball 82, as shown in FIG. 13(b). Thecross-shaped partition protrusion 86 consists of two partition wallswhich are perpendicular to each other and intersect at right angles fordividing a space in the dimple 14 into four segmental spaces. Each ofthe two partition walls has a thickness of, for example, about 0.5-1.5mm. The cross-shaped partition protrusion 86 has a distal end whoseradial distance from the center of the ball 82 is equal to the radius ofthe ball 82. Thus, the distal end of the cross-shaped partitionprotrusion 86 lies on the same surface as the spherical outer surface12. In the present eighth embodiment, the increased contact-areaportions 84 correspond to the hit portions. The ball 82 is put on thegreen in a preparation for putting the ball 82, such that one of theincreased contact-area portions 84 serves as the pressed area 22.

[0084] Where the golf ball 82 is pressed at the selected one of theincreased contact-area portions 84 by the putter face 20, thecross-shaped partition protrusion 86 constituting a part of an areainside each dimple 14, as well as an area surrounding each dimple 14, isbrought in contact with the putter face 20, thereby leading to a largercontact area provided in the pressed area 22, than where the ball 82 ispressed at the other portion of the spherical outer surface 12 in whichthe cross-shaped partition protrusions 86 are not provided, so that thedeviation of the center of balance of the contact area from the centerof the pressed area 22 tends to be reduced. Thus, by hitting the ball 82at the increased contact-area portion 84 in a putting stroke, it ispossible to make the center of the pressed area 22 substantiallycoincide with the center of balance of the contact area, i.e., thecenter of distribution of the reaction force applied from the ball 82 tothe putter face 20. Accordingly, the reaction force, which serves as athrust force for thrusting or moving the ball 82, is generated based ona restoring force of the ball 82 for restoring the pressed area 22 toits original shape, i.e., a part-spherical shape, and acts in adirection which is substantially parallel to the direction in which theputter head 18 is swung or stroked, thereby making it possible to puttthe ball 82 in a desired direction with an improved stability.

[0085] In the golf ball 82 of the present eighth embodiment of theinvention, a negative aerodynamic effect and a negative sensuous effectsuch as deterioration of the appearance are more reduced, owing to theprovision of the dimples 14 in the increased contact-area portions 84 aswell as in the other portions of the spherical outer surface 12, than inthe golf ball 10 of the above-described first embodiment having theundimpled portions 16 in which any one of the dimples 14 is notprovided.

[0086] While the presently preferred embodiments of this invention havebeen described in detail, for illustrative purpose only, it is to beunderstood that the present invention is not limited to the details ofthe illustrated embodiments, but may be otherwise embodied.

[0087] While the number of the hit portions (such as the undimpledportions 16, the single-dimple portions 42, the groove portions 54, 58,64, 72 and the increased contact-area portions 78, 84) is six in theabove-illustrated embodiments, the number of the hit portions may besuitably changed while taking account of, for example, a desired degreeof directional stability of the ball and a desired amount of lift orupward force acting on the ball during its flight in a golf course. Thatis, the object of the present invention can be achieved by providing theball with at least one hit portion which serves as the pressed area 22in a putting stroke. However, it is preferable to provide the ball witha plurality of hit portions, so that any one of the hit portions can beselected for serving as the pressed area 22, thereby facilitating apreparation for a putting stroke. Where the number of the hit portionsis two, the two hit portions preferably may be provided in respectivetwo portions which are diametrically opposite to each other, so as to besymmetrical with each other with respect to the center of the ball, sothat a center of balance of the hit portions coincides with the centerof the ball. Where the number of the hit portions is three, four orfive, too, the hit portions preferably may be arranged such that acenter of balance of the hit portions coincides with the center of theball. It is possible to increase the number of the hit portions as longas deterioration of performance of the ball in a golf course due to theincreased number is tolerable.

[0088] While the hit portions have the diameter of about 10 mm in theabove-illustrated embodiments, the diameter or size of the hit portionsmay range from about 5 mm to 15 mm, preferably from about 8 mm to 12 mm,depending upon, for example, a degree of elasticity of the ball.

[0089] The hit portions of the spherical outer surface 12 of the golfball of each of the above-illustrated embodiments are identical in formto each other. That is, the each of the hit portions take the form ofone of the undimpled portion 16, the single-dimple portion 42, thegroove portions 54, 58, 64, 72 and the increased contact-area portions78, 84. However, the hit portions of the spherical outer surface 12 ofthe golf ball may be different in form from each other.

[0090] The width of the grooves 52 of the lattice-arranged grooveportions 54, the annular grooves 56 of the annular groove portions 58,the grooves 62 of the parallel groove portions 64 or the grooves 68, 70of the groove portions 72 may range, for example, from 0.1 mm to 1.5 mm,depending upon various factors such as a desired degree of directionalstability and a desired amount of flight distance during its flight in agolf course. Similarly, the distance between the centers of the adjacentones of these grooves may range from 0.5 mm to 4 mm, depending upon thevarious factors. Further, the grooves may have the respective widthsdifferent from each other. The distance between the centers of theadjacent grooves does not necessarily have to be constant.

[0091] The diameter of the columnar protrusions 80 provided in theincreased contact-area portions 78 may be suitably changed as long asthe diameter of the columnar protrusions 80 is sufficiently smaller thanthe diameter of the dimples 14. While the columnar protrusions 80 havethe circular cylindrical shape in the above-illustrated embodiment, thecolumnar protrusions 80 may have a polygonal shape or other shape.

[0092] The thickness of the partition walls of the partition protrusions86 of the increased contact-area portions 84 may be suitably changed aslong as the thickness is sufficiently smaller than the diameter of thedimples 14. While the partition protrusions 86 have the cross shape inthe above-illustrated embodiment, the partition protrusions 86 may haveother shape which is suitable for dividing the space in each dimple 14into at least two segmental spaces.

[0093] The distal ends of the columnar-shaped protrusions 80 or thecross-shaped partition protrusions 86 do not have to lie on the samesurface as the spherical outer surface 12, but may be slightly protrudedor recessed from the spherical outer surface 12.

[0094] It is to be understood that the present invention may be embodiedwith various other changes, modifications and improvements, which mayoccur to those skilled in the art, without departing from the spirit andscope of the invention defined by the following claims:

What is claimed is:
 1. A golf ball having a predetermined radius, and aspherical outer surface with a multiplicity of dimples formed therein,wherein said spherical outer surface has at least one hit portion whichhas a diameter of 5-15 mm and within which said dimples are absent.
 2. Agolf ball according to claim 1 , wherein said at least one hit portionconsists of a plurality of hit portions which are positioned relative toeach other such that a center of balance of said plurality of hitportions coincides with the center of the golf ball.
 3. A golf ballaccording to claim 1 , wherein said diameter of said at least one hitportion is 8-12 mm.
 4. A golf ball having a predetermined radius, and aspherical outer surface with a multiplicity of dimples formed therein,wherein said spherical outer surface has at least one hit portion whichhas a diameter of 5-15 mm and within which said dimples are absentexcept a single one of said dimples that is located at a central part ofsaid hit portion.
 5. A golf ball according to claim 4 , wherein said atleast one hit portion consists of a plurality of hit portions which arepositioned relative to each other such that a center of balance of saidplurality of hit portions coincides with the center of the golf ball. 6.A golf ball according to claim 4 , wherein said diameter of said atleast one hit portion is 8-12 mm.
 7. A golf ball having a predeterminedradius, and a spherical outer surface with a multiplicity of dimplesformed therein, wherein said spherical outer surface has at least onehit portion which has a diameter of 5-15 mm and within which saiddimples are absent, and wherein a plurality of grooves are formed withinsaid hit portion and are distributed evenly in the entirety of said hitportion, each of said grooves having a predetermined shape and a widthwhich is smaller, than a diameter of each of said dimples.
 8. A golfball according to claim 7 , wherein said at least one hit portionconsists of a plurality of hit portions which are positioned relative toeach other such that a center of balance of said plurality of hitportions coincides with the center of the golf ball.
 9. A golf ballaccording to claim 7 , wherein said diameter of said at least one hitportion is 8-12 mm.
 10. A golf ball according to claim 7 , wherein saidgrooves are arranged in a lattice and intersect each other.
 11. A golfball according to claim 7 , wherein said grooves are annular grooveshaving respective diameters different from each other and respectivecenters lying at a center of said hit portion.
 12. A golf ball accordingto claim 7 , wherein said grooves are arranged to be parallel to eachother.
 13. A golf ball having a predetermined radius, and a sphericalouter surface with a multiplicity of dimples formed therein, whereinsaid spherical outer surface has at least one hit portion which has adiameter of 5-15 mm and within which a protrusion is formed in each ofsaid dimples, said protrusion having a distal end whose radial distancefrom the center of the golf ball is equal to said predetermined radiusof the golf ball.
 14. A golf ball according to claim 13 , wherein saidat least one hit portion consists of a plurality of hit portions whichare positioned relative to each other such that a center of balance ofsaid plurality of hit portions coincides with the center of the golfball.
 15. A golf ball according to claim 13 , wherein said diameter ofsaid at least one hit portion is 8-12 mm.
 16. A golf ball according toclaim 13 , wherein said protrusion is positioned relative to said eachof said dimples such that said protrusion has a concentric relation withsaid each of said dimples.
 17. A golf ball according to claim 13 ,wherein said protrusion has a partition wall which divides a space ineach of said dimples into a plurality of segmental spaces.